1. Technical Field
The present invention relates to: a light source device used as a light source of a display apparatus such as a liquid crystal display apparatus; and a display apparatus including the light source device.
2. Description of Related Art
In recent years, display apparatuses such as liquid crystal displays and liquid crystal televisions have widely been spread. A display apparatus includes a rectangular plate-shaped display panel which has a display surface at the front side on which an image is displayed, and a light source device disposed at the rear side of the display panel to irradiate the display panel with light. An example of the light source device includes a direct type light source device as disclosed in Japanese Patent Application Laid-Open No. 2008-58709. The light source device disclosed in Japanese Patent Application Laid-Open No. 2008-58709 is configured to include a light source such as a light emitting diode (LED) or a cold cathode fluorescent lamp (CCFL) disposed at the bottom of a dish-shaped casing and an optical sheet fixed at the opening portion of the casing. Moreover, the display apparatus disclosed in Japanese Patent Application Laid-Open No. 2008-58709 is so configured that a light source device is attached to a display panel such that the optical sheet faces the rear side of the display panel. In such a display apparatus, light from the light source is diffused by the optical sheet before entering the display panel. Further, in the light source device disclosed in Japanese Patent Application Laid-Open No. 2008-58709, a peripheral edge part of the optical sheet is held between a casing (support member) and a pressing member, while the pressing member which presses the optical sheet to the casing is made of a heat deformable material.
The optical sheet is generally made of synthetic resin, and may be shifted by oscillation during transportation if the attachment thereof to the casing is insufficient, which may damage the surface of the optical sheet. It is therefore desirable to firmly fix the optical sheet to the casing so as not to move during transportation.
When the display apparatus is in use, on the other hand, light emitted by the light source generates heat and the heat from the light source causes the optical sheet to expand, which causes wrinkles on the optical sheet expanded by the heat if the optical sheet is firmly fixed to the casing. In order to suppress the occurrence of wrinkles, it is desirable not to firmly fix the optical sheet but to fix it in such a manner that the expanded optical sheet has a margin to spread in the surrounding area.
In the light source device disclosed in Japanese Patent Application Laid-Open No. 2008-58709, a pressing member which presses the optical sheet to the casing is made of a heat deformable material, which increases the pressing force by the pressing member when the light source is turned off and decreases the pressing force by the pressing member when the light source is turned on.